Latest update on chemokine receptors as therapeutic targets

Identification and preliminary validation of differently expressed genes as candidate biomarkers associated with atherosclerosis

OBJECTIVE

Atherosclerosis (AS) is the primary cause of deadly cardio-cerebro vascular diseases globally. This study aims to explore the key differentially expressed genes (DEGs), potentially serving as predictive biomarkers for AS.

METHODS

Microarray datasets were retrieved from the GEO database for DEGs and DE-miRNAs identification. Then biological function of DEGs were elucidated based on gene ontology (GO) and KEGG pathway enrichment analysis. The protein-protein interaction (PPI) network and DEGs-DE-miRNAs network were constructed, with emphasis on hub DEGs selection and their interconnections. Additionally, receiver operating characteristic (ROC) curve analysis was performed to evaluate the diagnostic precision of hub DEGs for AS. More importantly, an AS Syrian Golden hamster model was established to validate the expression levels of hub DEGs in AS.

RESULTS

A total of 203 DEGs and 10 DE-miRNAs were screened, with six genes were chosen as hub DEGs. These DEGs were significantly enriched in AS-related biological processes and pathways, such as immune and inflammatory response, cellular response to IL-1 and TNF, positive regulation of angiogenesis, Type I diabetes mellitus, Cytokine-cytokine receptor interaction, TLR signaling pathway. Also, these DEGs and DE-miRNAs formed a closely-interacted DE-miRNAs - DEGs - KEGG pathway network. Besides, hub DEGs presented promising diagnostic potential for AS (AUC: 0.781 ∼ 0.887). In addition, the protein expression levels of TNF-α, CXCL8, CCL4, IL-1β, CCL3 and CCR8 were significantly increased in AS group Syrian Golden hamsters.

CONCLUSION

The identified candidate genes TNF, CXCL8, CCL4, IL1B, CCL3 and CCR8 may have the potential to serve as prognostic biomarker in diagnosing AS.

Advancing chemokine research: the molecular function of CXCL8

CXCL8 and other chemokines have been implicated in tissue inflammation and are attractive candidates for therapeutic targeting to treat human disease.

Neuroimmune modulation by tryptophan derivatives in neurological and inflammatory disorders

The nervous and immune systems are highly developed, and each performs specialized physiological functions. However, they work together, and their dysfunction is associated with various diseases. Specialized molecules, such as neurotransmitters, cytokines, and more general metabolites, are essential for the appropriate regulation of both systems. Tryptophan, an essential amino acid, is converted into functional molecules such as serotonin and kynurenine, both of which play important roles in the nervous and immune systems. The role of kynurenine metabolites in neurodegenerative and psychiatric diseases has recently received particular attention. Recently, we found that hyperactivity of the kynurenine pathway is a critical risk factor for septic shock. In this review, we first outline neuroimmune interactions and tryptophan derivatives and then summarized the changes in tryptophan metabolism in neurological disorders. Finally, we discuss the potential of tryptophan derivatives as therapeutic targets for neuroimmune disorders.

Molecular determinants of antagonist interactions with chemokine receptors CCR2 and CCR5

By driving monocyte chemotaxis, the chemokine receptor CCR2 shapes inflammatory responses and the formation of tumor microenvironments. This makes it a promising target in inflammation and immuno-oncology; however, despite extensive efforts, there are no FDA-approved CCR2-targeting therapeutics. Cited challenges include the redundancy of the chemokine system, suboptimal properties of compound candidates, and species differences that confound the translation of results from animals to humans. Structure-based drug design can rationalize and accelerate the discovery and optimization of CCR2 antagonists to address these challenges. The prerequisites for such efforts include an atomic-level understanding of the molecular determinants of action of existing antagonists. In this study, using molecular docking and artificial-intelligence-powered compound library screening, we uncover the structural principles of small molecule antagonism and selectivity towards CCR2 and its sister receptor CCR5. CCR2 orthosteric inhibitors are shown to universally occupy an inactive-state-specific tunnel between receptor helices 1 and 7; we also discover an unexpected role for an extra-helical groove accessible through this tunnel, suggesting its potential as a new targetable interface for CCR2 and CCR5 modulation. By contrast, only shape complementarity and limited helix 8 hydrogen bonding govern the binding of various chemotypes of allosteric antagonists. CCR2 residues S1012.63 and V2446.36 are implicated as determinants of CCR2/CCR5 and human/mouse orthosteric and allosteric antagonist selectivity, respectively, and the role of S1012.63 is corroborated through experimental gain-of-function mutagenesis. We establish a critical role of induced fit in antagonist recognition, reveal strong chemotype selectivity of existing structures, and demonstrate the high predictive potential of a new deep-learning-based compound scoring function. Finally, this study expands the available CCR2 structural landscape with computationally generated chemotype-specific models well-suited for structure-based antagonist design.

CXCR2 chemokine receptor - a master regulator in cancer and physiology

Recent findings have modified our understanding of the roles of chemokine receptor CXCR2 and its ligands in cancer, inflammation, and immunity. Studies in Cxcr2 tissue-specific knockout mice show that this receptor is involved in, among other things, cancer, central nervous system (CNS) function, metabolism, reproduction, COVID-19, and the response to circadian cycles. Moreover, CXCR2 involvement in neutrophil function has been revisited not only in physiology but also for its major contribution to cancers. The recent unfolding of the role of CXCR2 in numerous cancers has led to extensive evaluation of multiple CXCR2 antagonists in preclinical and clinical studies. In this review we discuss the potential of targeting CXCR2 for cancer treatment.

The role of PKC and PKD in CXCL12 and CXCL13 directed malignant melanoma and acute monocytic leukemic cancer cell migration

Cancer metastasis is the leading cause of cancer related mortality. Chemokine receptors and proteins in their downstream signalling axis represent desirable therapeutic targets for the prevention of metastasis. Despite this, current therapeutics have experienced limited success in clinical trials due to a lack of insight into the downstream signalling pathway of specific chemokine receptor cascades in different tumours. In this study, we investigated the role of protein kinase C (PKC) and protein kinase D (PKD) in CXCL12 and CXCL13 stimulated SK-MEL-28 (malignant melanoma) and THP-1 (acute monocytic leukaemia) cell migration. While PKC and PKD had no active role in CXCL12 or CXCL13 stimulated THP-1 cell migration, PKC and PKD inhibition reduced CXCL12 stimulated migration and caused profound effects upon the cytoskeleton of SK-MEL-28 cells. Furthermore, only PKC and not PKD inhibition reduced CXCL13 stimulated migration in SK-MEL-28 cells however PKC inhibition failed to stimulate any changes to the actin cytoskeleton. These findings indicate that PKC inhibitors would be a useful therapeutic for the prevention of both CXCL12 and CXCL13 stimulated migration and PKD inhibitors for CXCL12 stimulated migration in malignant melanoma.

Tryptophan metabolism as a 'reflex' feature of neuroimmune communication: Sensor and effector functions for the indoleamine-2, 3-dioxygenase kynurenine pathway

Although the central nervous system (CNS) and immune system were regarded as independent entities, it is now clear that immune system cells can influence the CNS, and neuroglial activity influences the immune system. Despite the many clinical implications for this 'neuroimmune interface', its detailed operation at the molecular level remains unclear. This narrative review focuses on the metabolism of tryptophan along the kynurenine pathway, since its products have critical actions in both the nervous and immune systems, placing it in a unique position to influence neuroimmune communication. In particular, since the kynurenine pathway is activated by pro-inflammatory mediators, it is proposed that physical and psychological stressors are the stimuli of an organismal protective reflex, with kynurenine metabolites as the effector arm co-ordinating protective neural and immune system responses. After a brief review of the neuroimmune interface, the general perception of tryptophan metabolism along the kynurenine pathway is expanded to emphasize this environmentally driven perspective. The initial enzymes in the kynurenine pathway include indoleamine-2,3-dioxygenase (IDO1), which is induced by tissue damage, inflammatory mediators or microbial products, and tryptophan-2,3-dioxygenase (TDO), which is induced by stress-induced glucocorticoids. In the immune system, kynurenic acid modulates leucocyte differentiation, inflammatory balance and immune tolerance by activating aryl hydrocarbon receptors and modulates pain via the GPR35 protein. In the CNS, quinolinic acid activates N-methyl-D-aspartate (NMDA)-sensitive glutamate receptors, whereas kynurenic acid is an antagonist: the balance between glutamate, quinolinic acid and kynurenic acid is a significant regulator of CNS function and plasticity. The concept of kynurenine and its metabolites as mediators of a reflex coordinated protection against stress helps to understand the variety and breadth of their activity. It should also help to understand the pathological origin of some psychiatric and neurodegenerative diseases involving the immune system and CNS, facilitating the development of new pharmacological strategies for treatment.

The development of potent, competitive CXCR4 antagonists for the prevention of cancer metastasis

Cancer metastasis is the cause of up to 90 % of cancer related mortality. The CXCR4 receptor and its cognate ligand, CXCL12, have major roles in enabling cancer metastasis and consequently, the CXCR4 receptor has become an attractive therapeutic target for the prevention of metastasis. Despite this, CXCR4 antagonists have had limited success in clinical trials due to cellular toxicity and poor stability and efficacy. In this study, we developed a novel, competitive CXCR4 antagonist (IS4) that through copper-catalysed-azide-alkyne-cycloaddition can be clicked to other chemical moieties such as fluorescent dyes (IS4-FAM) for CXCR4-based imaging. We determined that these CXCR4 antagonists were non-toxic and could be used to specifically label the CXCR4 receptor. Furthermore, IS4 and IS4-FAM inhibited CXCL12-stimulated cancer cell migration and Ca2+ release in both adherent and suspension cell lines with similar or improved potency as compared to two literature CXCR4 antagonists. Our results highlight the potential of IS4 and IS4-FAM as research tools and as potent CXCR4 antagonists for the prevention of metastasis.

The screening, identification, design and clinical application of tumor-specific neoantigens for TCR-T cells

Recent advances in neoantigen research have accelerated the development of tumor immunotherapies, including adoptive cell therapies (ACTs), cancer vaccines and antibody-based therapies, particularly for solid tumors. With the development of next-generation sequencing and bioinformatics technology, the rapid identification and prediction of tumor-specific antigens (TSAs) has become possible. Compared with tumor-associated antigens (TAAs), highly immunogenic TSAs provide new targets for personalized tumor immunotherapy and can be used as prospective indicators for predicting tumor patient survival, prognosis, and immune checkpoint blockade response. Here, the identification and characterization of neoantigens and the clinical application of neoantigen-based TCR-T immunotherapy strategies are summarized, and the current status, inherent challenges, and clinical translational potential of these strategies are discussed.

Identification of a Salt Bridge That Is Functionally Important for Chemokine Receptor CXCR1 but not CXCR2

CXC chemokine receptors 1 (CXCR1) and 2 (CXCR2) have high sequence similarity and overlapping chemokine ligand profiles. Residue positions 3.32 and 7.39 are critical for signal transduction in the related CXCR4, and in these positions CXCR1 and CXCR2 contain oppositely charged residues (Lys3.32 and Glu7.39). Experimental and computed receptor structures reveal the possible formation of a salt bridge between transmembrane (TM) helices 3 and 7 via these two residues. To investigate the functional importance of Lys1173.32 and Glu2917.39 in CXCR1, along with the flanking Glu1183.33, we performed a signaling study on 16 CXCR1 mutants using two different CXCL8 isoforms. While single Ala-mutation (K1173.32A, E2917.39A) and charge reversal (K1173.32E, E2917.39K) resulted in nonfunctional receptors, double (K1173.32E-E2917.39K) and triple (K1173.32E-E1183.33A-E2917.39K) mutants rescued CXCR1 function. In contrast, the corresponding mutations did not affect the CXCR2 function to the same extent. Our findings show that the Lys3.32-Glu7.39 salt bridge between TM3 and -7 is functionally important for CXCR1 but not for CXCR2, meaning that signal transduction for these highly homologous receptors is not conserved.

Chemokine Heteromers and Their Impact on Cellular Function-A Conceptual Framework

Chemoattractant cytokines or chemokines are proteins involved in numerous biological activities. Their essential role consists of the formation of gradient and (immune) cell recruitment. Chemokine biology and its related signaling system is more complex than simple ligand-receptor interactions. Beside interactions with their cognate and/or atypical chemokine receptors, and glycosaminoglycans (GAGs), chemokines form complexes with themselves as homo-oligomers, heteromers and also with other soluble effector proteins, including the atypical chemokine MIF, carbohydrate-binding proteins (galectins), damage-associated molecular patterns (DAMPs) or with chemokine-binding proteins such as evasins. Likewise, nucleic acids have been described as binding targets for the tetrameric form of CXCL4. The dynamic balance between monomeric and dimeric structures, as well as interactions with GAGs, modulate the concentrations of free chemokines available along with the nature of the gradient. Dimerization of chemokines changes the canonical monomeric fold into two main dimeric structures, namely CC- and CXC-type dimers. Recent studies highlighted that chemokine dimer formation is a frequent event that could occur under pathophysiological conditions. The structural changes dictated by chemokine dimerization confer additional biological activities, e.g., biased signaling. The present review will provide a short overview of the known functionality of chemokines together with the consequences of the interactions engaged by the chemokines with other proteins. Finally, we will present potential therapeutic tools targeting the chemokine multimeric structures that could modulate their biological functions.

Emerging roles of a chemoattractant receptor GPR15 and ligands in pathophysiology

Chemokine receptors play a central role in the maintenance of immune homeostasis and development of inflammation by directing leukocyte migration to tissues. GPR15 is a G protein-coupled receptor (GPCR) that was initially known as a co-receptor for human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV), with structural similarity to other members of the chemoattractant receptor family. Since the discovery of its novel function as a colon-homing receptor of T cells in mice a decade ago, GPR15 has been rapidly gaining attention for its involvement in a variety of inflammatory and immune disorders. The recent identification of its natural ligand C10orf99, a chemokine-like polypeptide strongly expressed in gastrointestinal tissues, has established that GPR15-C10orf99 is a novel signaling axis that controls intestinal homeostasis and inflammation through the migration of immune cells. In addition, it has been demonstrated that C10orf99-independent functions of GPR15 and GPR15-independent activities of C10orf99 also play significant roles in the pathophysiology. Therefore, GPR15 and its ligands are potential therapeutic targets. To provide a basis for the future development of GPR15- or GPR15 ligand-targeted therapeutics, we have summarized the latest advances in the role of GPR15 and its ligands in human diseases as well as the molecular mechanisms that regulate GPR15 expression and functions.

CCL21/CCR7 axis as a therapeutic target for autoimmune diseases

Chemokine receptor 7 (CCR7) is a G protein-coupled receptor containing 7 transmembrane domains that is expressed on various cells, such as naive T/B cells, central memory T cells, regulatory T cells, immature/mature dendritic cells (DCs), natural killer cells, and a minority of tumor cells. Chemokine ligand 21 (CCL21) is the known high-affinity ligand that binds to CCR7 and drives cell migration in tissues. CCL21 is mainly produced by stromal cells and lymphatic endothelial cells, and its expression is significantly increased under inflammatory conditions. Genome-wide association studies (GWAS) have shown a strong association between CCL21/CCR7 axis and disease severity in patients with rheumatoid arthritis, sjogren's syndrome, systemic lupus erythematosus, polymyositis, ankylosing spondylitis, and asthma. Disrupting CCL21/CCR7 interaction with antibodies or inhibitors prevents the migration of CCR7-expressing immune and non-immune cells at the site of inflammation and reduces disease severity. This review emphasizes the importance of the CCL21 /CCR7 axis in autoimmune diseases and evaluates its potential as a novel therapeutic target for these conditions.

Atypical chemokine receptors: emerging therapeutic targets in cancer

Atypical chemokine receptors (ACKRs) regulate the availability of chemokines via chemokine scavenging, while also having the capacity to elicit downstream function through β-arrestin coupling. This contrasts with conventional chemokine receptors that directly elicit immune cell migration through G protein-coupled signaling. The significance of ACKRs in cancer biology has previously been poorly understood, but recent findings have highlighted the multifaceted role of these receptors in tumorigenesis and immune response modulation within the tumor microenvironment (TME). Additionally, recent research has expanded our understanding of the function of several receptors including GPR182, CCRL2, GPR1, PITPNM3, and C5aR2 that share similarities with the ACKR family. In this review, we discuss these recent developments, and highlight the opportunities and challenges of pharmacologically targeting ACKRs in cancer.

Small molecule-based immunomodulators for cancer therapy

Immunotherapy has led to a paradigm shift in the treatment of cancer. Current cancer immunotherapies are mostly antibody-based, thus possessing advantages in regard to pharmacodynamics (e.g., specificity and efficacy). However, they have limitations in terms of pharmacokinetics including long half-lives, poor tissue/tumor penetration, and little/no oral bioavailability. In addition, therapeutic antibodies are immunogenic, thus may cause unwanted adverse effects. Therefore, researchers have shifted their efforts towards the development of small molecule-based cancer immunotherapy, as small molecules may overcome the above disadvantages associated with antibodies. Further, small molecule-based immunomodulators and therapeutic antibodies are complementary modalities for cancer treatment, and may be combined to elicit synergistic effects. Recent years have witnessed the rapid development of small molecule-based cancer immunotherapy. In this review, we describe the current progress in small molecule-based immunomodulators (inhibitors/agonists/degraders) for cancer therapy, including those targeting PD-1/PD-L1, chemokine receptors, stimulator of interferon genes (STING), Toll-like receptor (TLR), etc. The tumorigenesis mechanism of various targets and their respective modulators that have entered clinical trials are also summarized.

An integrated cytokine and kynurenine network as the basis of neuroimmune communication

Two of the molecular families closely associated with mediating communication between the brain and immune system are cytokines and the kynurenine metabolites of tryptophan. Both groups regulate neuron and glial activity in the central nervous system (CNS) and leukocyte function in the immune system, although neither group alone completely explains neuroimmune function, disease occurrence or severity. This essay suggests that the two families perform complementary functions generating an integrated network. The kynurenine pathway determines overall neuronal excitability and plasticity by modulating glutamate receptors and GPR35 activity across the CNS, and regulates general features of immune cell status, surveillance and tolerance which often involves the Aryl Hydrocarbon Receptor (AHR). Equally, cytokines and chemokines define and regulate specific populations of neurons, glia or immune system leukocytes, generating more specific responses within restricted CNS regions or leukocyte populations. In addition, as there is a much larger variety of these compounds, their homing properties enable the superimposition of dynamic variations of cell activity upon local, spatially limited, cell populations. This would in principle allow the targeting of potential treatments to restricted regions of the CNS. The proposed synergistic interface of 'tonic' kynurenine pathway affecting baseline activity and the superimposed 'phasic' cytokine system would constitute an integrated network explaining some features of neuroimmune communication. The concept would broaden the scope for the development of new treatments for disorders involving both the CNS and immune systems, with safer and more effective agents targeted to specific CNS regions.

Spotlight on liver macrophages for halting liver disease progression and injury

INTRODUCTION

Over the past two decades, understanding of hepatic macrophage biology has provided astounding details of their role in the progression and regression of liver diseases. The hepatic macrophages constitute resident macrophages, Kupffer cells, and circulating bone marrow monocyte-derived macrophages, which play a diverse role in liver injury and repair. Imbalance in the macrophage population leads to pathological consequences and is responsible for the initiation and progression of acute and chronic liver injuries. Further, distinct populations of hepatic macrophages and their high heterogeneity make their complex role enigmatic. The unique features of distinct phenotypes of macrophages have provided novel biomarkers for defining the stages of liver diseases. The distinct mechanisms of hepatic macrophages polarization and recruitment have been at the fore front of research. In addition, the secretome of hepatic macrophages and their immune regulation has provided clinically relevant therapeutic targets.

AREAS COVERED

Herein we have highlighted the current understanding in the area of hepatic macrophages, and their role in the progression of liver injury.

EXPERT OPINION

It is essential to ascertain the physiological and pathological role of evolutionarily conserved distinct macrophage phenotypes in different liver diseases before viable approaches may see a clinical translation.

The Chemokine (C-C Motif) Receptor 2 Antagonist INCB3284 Reduces Fluid Requirements and Protects From Hemodynamic Decompensation During Resuscitation From Hemorrhagic Shock

Clinical correlations suggest that systemic chemokine (C-C motif) ligand (CCL) 2 release may contribute to blood pressure regulation and the development of hemodynamic instability during the early inflammatory response to traumatic-hemorrhagic shock. Thus, we investigated whether blockade of the principal CCL2 receptor chemokine (C-C motif) receptor (CCR) 2 affects blood pressure in normal animals, and hemodynamics and resuscitation fluid requirements in hemorrhagic shock models.